5K sequence/footage scaled down with 2K footage into 1080 project

I have a 5K project with color renders at 5K (5120x2160). I'm editing the sequence (project) and then I'm going to duplicate the sequence and change the settings to 1080 for delivery (adding a black matte for the 2.37 crop).

The only different media I have is a single clip that has some compositing work done. It was rendered at 2560x1080 because the effect done looks different when scaled down from 5K.

My question is, when I scale down a sequence (project) will it scale the different resolution clip accordingly? Or will there be additional compression on the lower pixel ratio clip?

I'm having a hard time understanding this "fit - fill - none" setting in the inspector. I think I understand it, but I wish those settings would apply what it's doing to the scale in inspector so you could see a literal interpretation of what it's doing to X and Y scale.

[Jason Brown]"I think I understand it, but I wish those settings would apply what it's doing to the scale in inspector so you could see a literal interpretation of what it's doing to X and Y scale."

But that would make things harder when using Proxy media.

Proxy media can contain elements that are the same aspect ratio, but different frame size. It's means that if your are editing 960x540 proxies in a 1080 timeline, every clip would have a 2x scale added to it. When you then switched to full res 1080 media, that would mean that each 1080 clip would be double the size it needs to be. Add to that the center point coordinates and keyframe pixel values and things can get messy. This is why those settings exist as you can still correct the footage for the ultimate frame size without having to adjust parameters.

To answer your question, if you are going to scale the clips with the scale parameter, it will scale everything equally.

You will have to adjust the one 2k clip manually or add another instance of the clip to the sequence spearately.

In my workflow if I have a different delivery requirement than what I created my timeline, I simply create a compound clip and place that in the format/resolution of my delivery specs.

For example I edited a spot which was made up of combination of SD PAL anamorphic footage, 720p animations and a few 1080p shots. It was very heavy in compositing as I challenged myself to see if I could pull off a decent amount of motion graphics and even repair work just in FCP X. I went ahead and edited the spot in a SD Anamorphic timeline. Then I create a compound clip and then placed that in my delivery format 1080i, 29.97. FCP X uprezed the SD PAL anamorphic footage surprisingly well, did a respectable frame rate conversion to 1080i, and kept the 1080p shots looking pristine in the 1080i timeline. Frankly, the workflow was so simple it was a bit concerned. To my amazement FCP X did a tremendous job.

Of course you can change the resolution of an already edited timeline but run the risk of something going wrong with compositing, keyframing, or any reframing. I've seen it work several times, but a few others times it has been problematic.

I would try it both ways and see what gives you the best results for your workflow.